Download Temporo-Mandibular Joint Pain–Hyoid Muscles as the

TEMPORO-MANDIBULAR JOINT PAIN – HYOID MUSCLES AS THE SOURCE
Kerry J. Ridgway, BS, DVM, Certified Veterinary Acupuncturist
Equine Therapeutic Options
Aiken, South Carolina
INTRODUCTION:
As many as 70% of the horses in my practice that are presented for performance
oriented complementary medicine work-ups exhibit some degree of pain in the Temporomandibular joints. The pain may be expressed unilaterally or bilaterally. Many of the
cases seen have frequent recurrence. There are a number of etiologic mechanisms that
can trigger TMJ pain. They include: primary dental problems, bitting issues, a rider with
“hard hands,” an ill fitting saddle, tie downs, side reins, running reins, or simply a horse
who holds tension in the jaws. Over the past two years, I have come to recognize that
another very common source is hypertonicity of hyoid musculature. The issue with hyoid
musculature often persists after the other causes are ruled out or have had appropriate
therapy. All of the above factors may set up the hyoid tension and spasm.
ANATOMY AND BIOMECHANICS OF THE HYOID BONES AND MUSCLES
The key hyoid bones involved include the Lingual process of the Basihyoid, the
Basihyoid itself and the Ceratohyoid connecting the Basihyoid to the Stylohyoid bone.
Note that the Lingual process is centrally imbedded in the root of the tongue. This
structure is palpable through the tongue musculature and is approximately the size of
the 5th digit on a man’s hand. The examiner can then trace caudally and palpate the
anatomy of the Basihyoid bone. The Stylohyoid bone is a long thin bone 18 to 20
centimeters (seven to eight inches) in length extending from the Basihyoid (via the
Ceratohyoid) to connect via a rod of cartilage to the hyoid process of the petrous
temporal bone and the tympanic bulla.
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The sizeable Omohyoideus muscle originates under the scapula body on subscapsular
fascia. It inserts on the caudal end of the Lingual process of the Basihyoid bone. Its
action is to retract the tongue back to aid in swallowing. In the case of chronic
hypertonicity, it is pulling the tongue back in the throat without release and inhibiting
movement of the tongue. By virtue of the origin of the Omohyoideus, the muscle tension
limits the shoulder action as well. The other critical hyoid muscles that cause retraction
of the tongue and create too much tension in the shoulder are the Sternohyoideus m.
and the Sternothyroideus m.. When these muscles are retracted, the Stylohyoid muscle
and Occipitohyoid muscle contracts putting tension on the Temporo-mandibular joint.
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A thorough examination will often show that there is also pain and tension in the
Sternocephalicus muscle. The Sternocephalicus originating at the manubrium of the
sternum and inserting on the ramus of the mandible, opens the mouth in normal
swallowing, flexes the neck and pulls the head downward. In a resistant horse it opens
the mouth and the chronic tension/hypertonicity adds TMJ dysfunction. The Longis
capitis muscle can also place the TMJ joint under chronic tension.
DIAGNOSIS OF TMJ PAIN
Reactivity found when the clinician puts pressure into the Masseter muscle one
centimeter cranio-ventral to the TMJ (location of acupuncture point Stomach 8) This
point is indicative of pain in the TMJ. TMJ pain may also show as pain lateral to the
Occiput – C 1 junction (location of acupuncture point Gallbladder 20). Traction cranially
and caudally will evoke a withdrawal response if TMJ pain is present.
DIAGNOSIS AND TREATMENT OF HYOID MUSCLE INVOLVEMENT IN TMJ PAIN
By reaching (with the palm up) under the ramus of the mandible (on the opposite side
from the examiner) near its cranial curve, the base of the tongue can be palpated by
bringing the fingers medially and dorsally. Within the base of the tongue the examiner
can palpate the mass of the Lingual Process of the Basihyoid bone. By gentle
manipulation (traction and release) toward the examiner one can mobilize the bone and
the root of the tongue. Even gentle traction and manipulation may evoke a fairly strong
evasive action. Persistent gentle massage and traction and mobilization will accomplish
a myofascial release of the involved musculature. Release is often followed by a good
head shake and paroxysmal yawning. Evaluation and mobilization via the Lingual
process should be accomplished on both sides.
After accomplishing the releases the examiner can re-check the reactive acupuncture
points described above as well as tractioning of the mandible to be sure that the points
and TMJ pain has been ameliorated. Some horses may be so painful and reactive that
they are reluctant to allow manipulation of the Lingual process. In those cases it is
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advisable to first palpate under the scapula and effect a myofascial release at the origin
of the Omohyoideus m. (under and caudal to the Ascending pectoral m. (Subclavian m.)
by doing a set and hold into the subscapular fascia. This is accomplished by flexing the
head and neck toward the examiner and entering the open palm under the scapula. The
lower the head the easier it is to get behind the scapula. This release may require two to
three minutes of hold. It is not uncommon to hear “audibles” as the tension on the lower
cervicals is released. Again check to see that the pain in the TMJ is relieved.
The results of this procedure are very gratifying. The client or groom can be instructed
on how to perform the procedure. Follow up releases should be done for at least twice
weekly for two weeks and thereafter by palpation and evaluation of the mobility of the
Lingual process.
It is, of course, important to discover and remove the inciting cause to effect long term
relief. This would include evaluation of the appropriateness of the bit, the horse’s
reaction to the bit and to the rider’s hands and use of side reins, etc.. It is also important
to check for concurrent dental problems. Other considerations were listed in the first
paragraph of this paper.
The author has had success in specific cases to ameliorating the condition where horses
want to hang the tongue outside of the mouth.
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